1. Field of the Invention
This invention relates to a device useful during orthodontic treatment for repositioning the mandibular jaw. More specifically, this invention relates to a mandibular repositioning device for urging the lower jaw in a forward direction relative to the upper jaw in order to improve occlusion.
2. Description of the Related Art
Orthodontic treatment involves movement of malpositioned teeth to orthodontically correct positions. During treatment, tiny orthodontic appliances known as brackets are often connected to anterior, cuspid and bicuspid teeth, and an archwire is placed in a slot of each bracket. The archwire forms a track to guide movement of the brackets and the associated teeth to desired positions for correct occlusion. Typically, the ends of the archwire are held by appliances known as buccal tubes that are secured to the patient's molar teeth. The brackets, archwires and buccal tubes are commonly referred to as “braces”.
The orthodontic treatment of some patients include correction of the alignment of the upper dental arch with the lower dental arch. For example, certain patients have a condition referred to as a Class II malocclusion where the lower dental arch is located an excessive distance in a rearward direction relative to the location of the upper dental arch when the jaws are closed. Other patients may have an opposite condition referred to as a Class III malocclusion wherein the lower dental arch is located in a forward direction of its desired location relative to the position of the upper dental arch when the jaws are closed.
Orthodontic treatment of Class II malocclusions are commonly corrected by movement of the upper dental arch as a single unit relative to movement of the lower dental arch as a single unit. To this end, forces are often applied to each dental arch as a unit by applying force to the brackets or buccal tubes, the archwires, or attachments connected to the brackets, buccal tubes, or archwires. In this manner, a Class II malocclusion can be corrected at the same time that the archwires and the brackets are used to move individual teeth to desired positions relative to each other.
Correction of Class II malocclusions is sometimes carried out by use of a force-applying system known as headgear that includes strapping which extends around the rear of the patient's head. The strapping is often connected by tension springs that, in turn, are connected to the buccal tubes, the brackets or one of the archwires.
However, headgear is often considered unsatisfactory because it is visibly apparent. Headgear may serve as a source of embarrassment, particularly among child and teenage patients who may experience teasing from classmates. The embarrassment can be somewhat reduced if the orthodontist instructs the patient to wear the headgear only at night, but unfortunately such practice may lengthen treatment time since the desired corrective forces are applied during only a portion of each calendar day.
Consequently, many practitioners and patients favor the use of intra-oral devices for correcting Class II malocclusions. Such devices are often located near the cuspid, bicuspid and molar teeth and away from the patient's anterior teeth. As a result, intra-oral devices for correcting Class II malocclusions are hidden in substantial part once installed and eliminate much of the patient embarrassment that is often associated with headgear.
Orthodontic force modules made of an elastomeric material have been used in the past to treat Class II malocclusions by connecting a pair of such force modules between the dental arches on opposite sides of the oral cavity. Elastomeric force modules are often used in tension to pull the jaws together in a direction along references lines that extend between the points of attachment of each force module. Such force modules may be an O-ring or a chain-type module made of a number of integrally connected O-rings. However, these modules are typically removable by the patient for replacement when necessary, since the module may break or the elastomeric material may degrade during use to such an extent that the amount of tension exerted is not sufficient.
Unfortunately, orthodontic devices such as headgear and removable force modules are not entirely satisfactory for use with some patients, because the effectiveness of the devices is dependent upon the patient's cooperation. Neglect of the patient to faithfully wear the headgear each day or install new elastomeric force modules as appropriate can seriously retard the progress of treatment and defeat timely achievement of the goals of an otherwise well-planned treatment program, resulting in an additional expenditure of time for both the patient and the orthodontist.
As a result, a number of intra-oral devices that are non-removable by the patient have been proposed in the past to overcome the problems of patient cooperation associated with headgear and with removable intra-oral force modules. For example, U.S. Pat. Nos. 3,798,773, 4,462,800 and 4,551,095 disclose telescoping tube assemblies that urge the jaws toward positions of improved alignment. The assemblies are securely coupled to other orthodontic appliances such as brackets or buccal tubes by the practitioner, and the problems of patient non-compliance are avoided.
An improved telescoping, intra-oral force module is described in applicant's U.S. Pat. No. 5,964,588. This module includes a first tubular member, a second tubular member slidably received in the first member and a third member that is slidably received in the second member. A helical spring extends around the second member for urging the second member and the first member in directions away from each other. The three members allow the jaws to be opened widely without separation of one member relative to the other two members.
Other orthodontic devices for correcting Class II malocclusions are described in U.S. Pat. Nos. 4,708,646, 5,352,116, 5,435,721 and 5,651,672. The devices described in these references include flexible members that are connected to upper and lower jaws of a patient. The length of the members is selected such that the member is curved in an arc when the patient's jaws are closed. The members have an inherent bias that tends to urge the members toward a normally straight orientation to provide a force that pushes one jaw forwardly or rearwardly relative to the other jaw when the jaws are closed.
U.S. Pat. Nos. 5,645,424 and 5,678,990 describe intra-oral devices for correcting Class II malocclusions having linkage that includes pivotal connections. The devices in both of these references have a somewhat overall “Z”-shaped configuration. A device having a somewhat similar overall configuration is shown in U.S. Pat. No. 5,645,423 and includes double helical loops located on each side of a central segment. A device having a different configuration is set out in applicant's U.S. Pat. No. 5,980,247.
The intra-oral devices described in the aforementioned U.S. Pat. Nos. 5,645,423, 5,645,424 and 5,678,990 have outer arms or shanks for connection to respective tubes. One of the tubes is connected to a molar tooth of the patient's upper dental arch and the other tube is coupled to a molar tooth of the patient's lower dental arch. It is an advantage to connect such intra-oral devices to the molar teeth of both arches, because the relatively large size of the roots of the molar teeth provides a good anchoring location for applying forces to move one jaw relative to the other jaw.
Some practitioners have a preference to use a device that applies a spring force to one or both dental arches when the patient's jaws are closed. These devices are often constructed so that the patient does not experience a “hard stop” as the teeth come together. However, the biasing force provided by the spring tends to move the dental arches relative to each other over a period of time.
Other practitioners prefer to use a device that reaches a hard, fixed limit as the jaws are closed. An example of such a device is the Herbst appliance, which includes a telescoping tube assembly. It is sometimes believed that these devices are more effective in moving the arches relative to each other for a given length of treatment time, since the jaws must reposition themselves each time the jaws are closed. These devices are considered especially effective when the patient is relatively young and bone growth is still proceeding at a relatively fast rate.
However, some of the devices known in the past for repositioning the dental arches are considered to present problems when a hard stop is provided as the jaws are closed. Specifically, if the jaws tend to posture to a Class II relationship during jaw closure, the resulting forces on various appliances in the oral cavity can be significant. The strength of the muscles of mastication, and particularly the masseter muscle, can produce significant force as the jaws are closed. This force may fracture the device or other components connected to the device, or cause attachments such as brackets and buccal tubes to be detached from the teeth.
Fracture or detachment of the jaw repositioning devices or accompanying components during the course of treatment is a nuisance to both the practitioner and the patient. When breakage occurs, the patient should return immediately to the orthodontist for replacement of the broken components so that treatment can resume. There is also the possibility that the broken components may contact and injure the oral tissue and cause significant pain.
In the past, a common response to the problem of breakage as mentioned above has been to provide stronger components, such as larger and stiffer assemblies. In addition, crowns are sometimes placed over the molar teeth and used as attachments rather than buccal tubes so that the risk of detachment from the tooth is reduced. However, such modifications are not considered entirely satisfactory due to the increased bulk and expense of the replacement components.
In an article entitled “The Swedish-Style Integrated Herbst Appliance” by Drs. Paul Haegglund and Staffan Segerdal, The Journal of Clinical Orthodontics, June 1997, pages 378–390, the authors describe the use of a Herbst appliance that is connected on its lower end to an auxiliary archwire. The auxiliary archwire extends in parallel relationship to the lower archwire and is slidably received in auxiliary passages of lower buccal tubes mounted on each side of the mandibular arch. An anterior section of the auxiliary archwire is coupled by elastomeric modules to the lower, main archwire or to hooks connected to the lower archwire.
The elastomeric modules described in the preceding article served as a force limiting device that tended to reduce the probability of appliance breakage or detachment. However, the resistance to tensile forces of elastomeric modules may deteriorate over a period of time. In addition, the force limiting or shock-absorbing effect provided by the elastomeric modules is dependent on the freedom of the auxiliary archwire to slide in the auxiliary passages of the buccal tubes, and such sliding freedom may be hindered by the difficulty of sliding a curved section of the auxiliary archwire within a buccal tube passage that has a straight configuration.
As can be appreciated, there is a need in the orthodontic art for a new device that is effective in repositioning the jaws of patient with a Class II malocclusion. A device is needed that functions reliably and efficiently, and yet is not prone to breakage or likely to cause adjacent components such as buccal tubes to be detached from the associated teeth.